This invention relates to an improved intrachannel clarifier for use in clarifying an effluent in a waste water treatment facility such as an oxidation ditch.
Waste water which is treated in an activated sludge process is commonly continuously circulated around a channel of an oxidation ditch that acts as an aeration basin. Bacteria in the oxidation ditch decompose wastes in the waste water, and a clarifier is then used to remove solids from the waste water to form a clear effluent.
Recently. intrachannel clarifiers which are positioned within the oxidation ditch have been designed, as exemplified by the clarifiers described in the following U.S. Pat. Nos.: Stensel U.S. Pat. No. 4,303,516, Cerwick U.S. Pat. No. 4,446,018, Kersten U.S. Pat. No. 4,487,692, Morrow U.S. Pat. No. 4,455,239, Beard U.S. Pat. No. 4,383,922, Beard U.S. Pat. No. 4,362,625, Beard U.S. Pat. No. 4,436,632 and Beard U.S. Pat. No. 4,457,844. Several of these clarifiers are discussed in a paper entitled Assessment of Design Tradeoffs When Using Intrachannel Clarifiers. by Jon H. Bender (Water Pollution Control Federation, 59th Annual Conference, Los Angeles. Calif. Oct. 6-9, 1986).
All of the intrachannel clarifiers described in the above-identified documents rely on settling processes to remove solids through ports in the bottom of the clarifier. The clarifiers shown in the Cerwick, Morrow, Kersten and Beard patents rely entirely on passive settling processes to remove solids from the clarifier. The device shoWn in the Stensel patent uses a scraper system to move settled solids across a floor panel toward ports arranged along the sides of the floor panel.
When simple settling processes are relied upon to remove solids from an intrachannel clarifier, solids may remain suspended within the clarifier for an excessive period of time. When this happens, the solids can evolve gases which cause the solids to float. Such floating solids may contaminate the effluent and cause the clarifier to fail to remove solids from the effluent to a satisfactory degree. In order to reduce such problems, regular cleaning is often required to remove solids from the clarifier.
Furthermore, if an intrachannel clarifier occupies an excessive portion of the flow path of the oxidation ditch, the clarifier can act as a partial dam which reduces the flow velocity in the flow path and causes excessive settling of solids in the oxidation ditch itself. When this occurs, the energy required to mix and add oxygen to the ditch contents increases, and unusually frequent cleaning and maintenance of the oxidation ditch may be required.
The present invention is directed to an improved intrachannel clarifier which actively controls the residence time of solids within the clarifier in order to minimize problems related to solids-evolved gases and floating solids within the clarifier.